---Can you tell me something about your school rules?

---Well, We are told ______anywhere. It’s our duty to keep our school clean and tidy.

A．not to make much noise

B．to draw

C．to throw waste paper

D．not to spit

下列各式的变形中，是分解因式的为（　　）

A．3x（2x+5）=6x²+15x

B．2x²-x+1=x（2x-1）+1

C．x²-xy=x（x-y）

D．a²+b²=（a+b）（a-b）